Apparatus for maintaining constant flow resistance in a centrifugal extractor



A ril 16, 1963 F. T. E. PALMQVIST 3,08

APPARATUS FOR MAINTAINING CONSTANT FLOW RESISTANCE IN A CENTRIFUGALEXTRACTOR Filed Feb. 25. 1958 INVENTUR. fie ik f oo or manue/ Qo/mywslBy I .7,'. M vW -K AT T 0 R N E 1 3,085,742 APPARATUS FOR MAENTAININGQONSTANT FLOW RESKSTANQE IN A CENTRHFUGAL EXTRACTOR Fredrik TeodorEmanuel Palmqvist, Soina, Sweden, assignor to Aktiebolaget Separator,Stockholm, Sweden, a corporation of Sweden Filed Feb. 25, 1958, Ser. No.717,518 Qlaims priority, application Sweden Feb. 28, 1957 7 Claims. (Cl.23315) The present invention relates to an improved apparatus formaintaining constant flow resistance in the centrifugal extractoradapted for throughflow passage of two or more media which, during thethroughfiow, influence each other chemically or physically.

A centrifugal extractor is, in principle, a centrifugal separator inwhich an extraction process is carried out. An example of such aseparator is that disclosed in Swedish Patent No. 146,598 and thecorresponding US. Patent No. 2,879,282, issued March 24, 1959. In thisseparator, an extraction with the current is carried out in one step. Bycentrifugal extractors, however, is usually meant such apparatus inwhich an extraction is carried out in several steps andcountercurrently, mixing and separation taking place in each step.

The extractors mentioned above as examples are intended for use incontinuous operation. To this end, it is desirable that the extractionprocess for which the extractors are used be automatically regulated.According to the present invention, the variations which may occur inthe various extraction media during the extraction process are utilizedfor this purpose. These variations may appear in the form of a changedflow resistance or pressure drop in the extractor, due, for instance, toa change in the viscosity or the specific gravity of the media. A changein specific gravity thus causes a displacement of the boundary levelbetween the media with accompanying change of the throughflow areas forthem. A change in viscosity or specific gravity may indicate a change inthe extraction process, which change it is desired to avoid. As anexample may be mentioned washing of soap in an extractor with an aqueoussolution of an electrolyte. On certain conditions, theviscosity-electrolyte content curve in soap is U-shaped. This meansthat, in one case (one leg of the curve), the viscosity decreases whenthe electrolyte content of the soap is increased and, in another case(the other leg of the curve), the viscosity increases when theelectrolyte content of the soap is increased. A certain quality of thesoap corresponds to a certain viscosity in one of the legs of the curveor to a certain electrolyte content. Therefore, if it is desired tomaintain a certain quality of the soap leaving the extractor, it isnecessary to maintain a certain viscosity in the soap and, accordingly,a certain flow resistance or pressure drop in the extractor. Theadjustment of this quality may thus be effected by regulating theconcentration of the electrolyte solution flowing through the extractor.

The principal object of the present invention is to solve the regulatingproblem mentioned above.

An apparatus made according to the invention comprises a dosing meansfor feeding one of the media (herein called the first medium) throughthe extractor at a constant rate (constant quantity per unit of time), ameans for mainaining in the path of the first medium a constant pressureat the inlet to or the outlet from the extractor, a meter for thepressure drop of the first medium during the how through the extractor,a means for maintaining in the path of the second medium a constantpressure at the inlet to or the outlet from the extractor, and a deviceoperated by the indications of Patented Apr. 16, 1963' the pressure dropmeter for regulating the second medium as to its composition or itstemperature or the rate at which it is fed through the extractor. It isobvious that many different extraction processes can be regulated withthis apparatus, such as extraction of colored constituents and excesssulphuric acid from sulphonic acid for the manufacture of detergents,degumming of fatty oil with water (the viscosity of the gum is keptconstant), and refining of mineral oil with sulphuric acid (the specificgravity of the sludge is kept constant).

In one embodiment of the invention, means are provided for keeping aconstant pressure at the outlet of the first medium from the extractor,and the dosing means for the first medium is provided at the inlet ofthis medium into the extractor.

In another embodiment of the invention, means are provided for keeping aconstant pressure at the outlet of the second medium from the extractor,and the regulating device for the second medium is provided at the inletof this medium into the extractor.

It is advantageous to combine these two embodiments, and in thiscombination embodiment it is possible to obtain a regulation of thecomposition of the second medium by arranging, between the regulatingdevice for this medium and the inlet of this medium into the extractor,a dosing means for feeding this medium through the extractor at aconstant rate, and by using as a regulating device a mixer having inletsfor two or more different components, at least one of these inlets beingarranged to be controlled by the indications of the pressure drop meter.

One or possibly both of the means for keeping constant pressure mayconsist merely of outlets from the extractor to the atmosphere. 'Ingeneral, however, it is preferable that one of such means consist of anoutlet to the atmosphere and the other of a means which keeps a constantpressure higher than the atmospheric pressure. Means of the latter kind(automatic valves) are well known.

The invention is described in greater detail in connection with theaccompanying drawing, in which FIGS. 1-5 are schematic views of variousembodiments.

Referring now to FIG. 1, the reference numeral 1 designates theextractor in which there are shown, for the sake of simplicity, only twoliquid layers 2 and 3, one of which is represented by a blank surfaceand the other by a hatched surface. In reality, these layers form twocylinders which are concentric with one another, and the drawingsymbolizes one half of an axial section through these cylindrical(actually somewhat conical) liquid layers. The layer 2 is assumed toconsist of the light liquid and the layer 3 of the heavy liquid,although the case could as well be in the reverse. The light liquid isfed into the extractor independently of the counter-pressure at aconstant rate (quantity by volume per unit of time) through a feed line4 by means of a dosing device or pump 5, such as a positive pump, forinstance a gear or piston pump. A positive pump means here a pump whosevolumetric throughput is proportional to the number of revolutions ofthe pump. From the extractor .1, the light liquid is fed out through adischarge line 6 against a constant pressure which is maintained bymeans such as a valve 7. The valve 7 may, if desired, be replaced by anoutlet to the free atmosphere, if this outlet opens at a suitable radialdistance from the axis of rotation of the extractor. The free atmospherehere also represents a constant pressure. In the feed line 4, betweenthe pump or dosing device 5 and the extractor 1, is a manometer 8 whoseindications, through an operative connection 9, actuate a regulator orcontrol device 10 in the feed line 11 for the heavy liquid. As thedischarge pressure for the light liquid is kept constant by the valvemeans 7, changes in the meter 8 indicate changes in the pressure dropwithin the extractor and, therefore, changes in the viscosity orspecific gravity of the liquids, as mentioned above. From the extractor,the heavy liquid leaves through a discharge line 12 which, at a distancefrom the axis of rotation of the extractor, opens through an outlet 13into the free atmosphere, the latter, as previously mentioned,representing a constant pressure. Thus, the vented outlet 13 constitutesin effect a means in the discharge line 12 for maintaining a constantpressure in this line.

Let it now be assumed that a disturbance occurs in the extractor, forinstance, because the viscosity of the light liquid increases so as tocause an undesired condition in the extraction process. The heavy liquidmust now be influenced in such a way as to restore the extractionprocess to the condition desired. When this has been done, the viscosityof the light liquid will have resumed its normal value. Assuming thatthe viscosity of the light liquid decreases as the temperature of theheavy liquid increases, the regulator 10 may be adapted to increase theheating of the heavy liquid when the viscosity of the light liquidincreases and the manometer 8 thus indicates an increased pressure.

Of course, the regulator 10 may also take the form of a flow regulator,if the quantity of the heavy liquid supplied per unit of time changesthe viscosity or the specific gravity of the light liquid.

The embodiment shown in FIG. 2 differs from that according to FIG. 1 inthat a constant pressure is kept at the inlet side for the heavy liquidby means in the form of a valve 14 and that the manometer 8 actuates acontrol device or regulator 10a in the discharge 11116.12. of the heavyliquid. The regulator 10a functions in this case to control thedischarge rate of heavy liquid from the extractor by regulating thethrottling of the line 12 in order to influence, as in the precedingcase, the viscosity or the specific gravity of the light liquid. On theother hand, this embodiment does not make it possible to influence thenature of the heavy liquid before entering the extractor.

In the FIG. 3 embodiment, the light liquid is fed into the extractor ata constant pressure through valve 7:: and is discharged at a constantrate through pump 5a. In this case, the constant pressure must be keptso high that, in spite of the pressure drop variations that may occurbefore the pump 5a, a pressure remains which is sufficiently high toensure that the pump 5:: always feeds out a fixed quantity per unit oftime. As to the heavy liquid, the circumstances here are the same as inthe FIG. 1 embodiment, except that the manometer 8a actuates theregulator from the discharge line 6 for the light liquid.

In the embodiment shown in FIG. 4, the apparatus associated with thelight liquid is the same as in FIG. 3, while the apparatus associatedwith the heavy liquid is the same as in FIG. 2, except that themanometer 8a in the FIG. 4 embodiment actuates the regulator 10a fromthe discharge line 6 for the light liquid.

The embodiment shown in FIG. 5 is similar to that shown in FIG. 1,except that in FIG. 5 the control device 10 is arranged to regmlate thecomposition or concentration of the heavy liquid. Here, the heavy liquidis assumed to be an aqueous solution of a salt. In the line 11 isinserted a pump 15 which feeds a constant quantity of liquid per unit oftime. The pump 15 is supplied with salt solution of fixed concentration,preferably concentrated salt solution, from a feed line 16 at a ratewhich is regulated by the control device or valve 10. Through a branchfeed line 17, the pump 15 is supplied by unrestricted inflow with waterat a rate corresponding to the difference between the throughput rate ofthe pump 15 and the rate of feed of salt solution through the line 16.

For a better understanding of the embodiment shown in FIG. 5, it may beassumed that a soap mass passes at a constant rate through the line 4from the saponifying stage in a continuously operating soap factory. Thesoap mass is presumed to be in such a condition that an increase in itsviscosity should be counteracted by increasing the salt content in anaqueous solution with which the soap is washed in the extractor 1. Thesoap, which in this case constitutes the lighter phase, corresponds tothe layer 2, while the salt solution constitutes the heavier phase andcorresponds to the layer 3. If the viscosity of the soap now increases,the manometer 8 indicates an increased pressure drop and actuates theregulator 10 through operating connection 9 to increase the supply ofsalt solution to the pump 15. As a result, the water quantity fed perunit of time to the pump 15 through the line 17 decreases. Thus, thesalt solution fed by the pump 15 into the extractor 1 will have its saltcontent increased. When the increase has become sufiicient, theviscosity of the soap decreases to the value desired so that theintended balance in the washing or extraction process is attained.

It will be understood that the constant pressure maintaining means 7(and 14) may be any conventional valve commonly used for this purpose.An example of such a valve is the diaphragm-operated valve in which thepressure on the diaphragm is varied through an operating connection 18from a device 19 which senses changes in the pressure to be maintainedconstant. Thus, in FIGS. 1 and 2, for example, a pressure decrease inline 6 acts through the sensing device 19 and connection 18 to move thediaphragm so as to throttle the valve 7 and thereby restore the pressureto the desired value.

The operating connection 9 from the manometer 8 to the control device 10may be any conventional systern for transmitting motion from anindicator to a remote control point, such as an electric or hydraulicservo system. As such systems are well known, a detailed description ofthe operating connection 9 is unnecessary.

Iclaim:

1. In combination with a centrifugal extractor through which first andsecond media are adapted to flow while contacting and influencing eachother, the extractor having separate feed and discharge lines for therespective media arranged to feed and discharge each medium separatelyto and from the centrifugal extractor, each line being located at oneend of the extractor; apparatus for maintaining a constant flowresistance in the centrifugal extractor, comprising a constant deliverypump in one of said separate lines for the first medium and operable tofeed said first medium through the extractor at a constant rate, meansfor maintaining a constant pressure in the other of said lines for thefirst medium, a pressure meter in said one line for the first medium andoperable to indicate a variation in the pressure drop of the firstmedium as it flows through the extractor, said one line for the firstmedium being closed to atmosphere throughout the length of said one linebetween the extractor and said pump and meter, means for maintaining aconstant pressure in one of said lines for the second medium, a controldevice in one of said lines for the second medium for so regulating thesecond medium in said flow thereof through the extractor as to influencethe flow resistance of said first medium, and an operative connectionbetween the control device and said meter and through which said deviceis operable by the meter in response to said variation to counteractsaid variation.

2. Apparatus according to claim 1, in which said pressure maintainingmeans for the first medium is in the discharge line for the firstmedium, said pump being in the feed line for the first medium.

3. Apparatus according to claim 1, in which said pressure maintainingmeans for the second medium is in the discharge line for the secondmedium, said control device being in the feed line for the secondmedium.

4. Apparatus according to claim 1, in which said pressure maintainingmeans for the first medium is in the discharge line for the firstmedium, said pump being in the feed line for the first medium, saidpressure maintaining means for the second medium being in the dischargeline for the second medium, and said control device being in the feedline for the second medium.

5. Apparatus according to claim 1, in which one of said pressuremaintaining means includes an outlet from the extractor opening toatmosphere.

6. Apparatus according to claim 1, in which one of said pressuremaintaining means includes an outlet from the extractor opening toatmosphere, the other of said pressure maintaining means including avalve for maintaining a constant pressure above atmospheric pressure.

7. Apparatus according to claim 1, in which the control device is avalve in the feed line for the second medium, the apparatus comprisingalso a branch feed linejoining said second medium feed line at a pointbetween said valve and the extractor, whereby the second medium includestwo components combined at said point, and a pump located in said secondmedium feed line between said point and the extractor and operable tofeed said second medium through the extractor at a constant rate.

References Cited in the file of this patent UNITED STATES PATENTS2,597,138 Trigg May 20, 1952 2,628,023 Dahlstedt Feb. 10, 1953 2,707,964Monroe May 10, 1955 2,758,783 Podbielniak Aug. 14, 1956 2,961,154 BergeyNov. 22, 1960

1. IN COMBINATION WITH A CENTRIFUGAL EXTRACTOR THROUGH WHICH FIRST ANDSECOND MEDIA ARE ADAPTED TO FLOW WHILE CONTACTING AND INFLUENCING EACHOTHER; THE EXTRACTOR HAVING SEPARATE FEED AND DISCHARGE LINES FOR THERESPECTIVE MEDIA ARRANGED TO FEED AND DISCHARGE EACH MEDIUM SEPARATELYTO AND FROM THE CENTRIFUGAL EXTRACTOR, EACH LINE BEING LOCATED AT ONEEND OF THE EXTRACTOR; APPARATUS FOR MAINTAINING A CONSTANT FLOWRESISTANCE IN THE CENTRIFUGAL EXTRACTOR, COMPRISING A CONSTANT DELIVERYPUMP IN ONE OF SAID SEPARATE LINES FOR THE FIRST MEDIUM AND OPERABLE TOFEED SAID FIRST MEDIUM THROUGH THE EXTRACTOR AT A CONSTANT RATE, MEANSFOR MAINTAINING A CONSTANT PRESSURE IN THE OTHER OF SAID LINES FOR THEFIRST MEDIUM, A PRESSURE METER IN SAID ONE LINE FOR THE FIRST MEDIUM ANDOPERABLE TO INDICATE A VARIATIONS IN THE PRESSURE DROP OF THE FIRSTMEDIUM AS IT FLOWS THROUGH THE EXTRACTOR, SAID ONE LINE FOR THE FIRSTMEDIUM BEING CLOSED TO ATMOSPHERE THROUGHOUT THE LENGTH OF SAID ONE LINEBETWEEN THE EXTRACTOR AND SAID PUMP AND METER, MEANS FOR MAINTAINING ACONSTANT PRESSURE IN ONE OF SAID LINES FOR THE SECOND MEDIUM, A CONTROLDEVICE IN ONE OF SAID LINES FOR THE SECOND MEDIUM FOR SO REGULATING THESECOND MEDIUM IN SAID FLOW THEREOF THROUGH THE EXTRACTOR AS TO INFLUENCETHE FLOW RESISTANCE OF SAID FIRST MEDIUM, AND AN OPERATIVE CONNECTIONBETWEEN THE CONTROL DEVICE AND SAID METER AND THROUGH WHICH SAID DEVICEIS OPERABLE BY THE METER IN RESPONSE TO SAID VARIATION TO COUNTERACTSAID VARIATION.